Physiological parameters for living beings are typically a function of one or more of the following: the time-of-day, environmental conditions to which a being is exposed, activity level of a being, and various other physiological parameters. Many of these are related. For example, the average change in heart rate, body temperature, and heart rate variability (HRV) with the time-of-day are generally known based on human and animal studies of the circadian cycle.